1. Field of the Invention
The present invention relates to a squeegee device and a screen printing machine used to print a solder on a circuit board.
2. Description of the Related Art
A screen printing machine includes a squeegee device and a screen mask. The squeegee device is arranged above the screen mask. The squeegee device includes a device body, a squeegee holder, and a squeegee. The squeegee is mounted on the squeegee holder. The screen mask is formed with pattern holes. A solder is arranged on the upper surface of the screen mask. A circuit board is arranged below the screen mask.
When printing a solder on the circuit board, first, the device body is lowered and the squeegee is pressed into contact with the upper surface of the screen mask. Next, the device body is moved in a substantially horizontal direction with respect to the upper surface of the screen mask. The squeegee slides against the upper surface of the screen mask. The squeegee presses the solder into the pattern holes. The pressed solder is transferred onto the circuit board. Thus, the solder is printed on the circuit board by the squeegee. Therefore, an attack angle of the squeegee (a narrow angle between the screen mask upper surface and the squeegee) is an important parameter for securing printing quality. The attack angle of the squeegee is modified as appropriate when changing the type of circuit board on which to print a solder, that is, during a tooling change.
According to related art, the type of squeegee holder is changed when changing the attack angle of the squeegee. Specifically, a plurality of types of squeegee holders with different attachment angles with respect to the device body is prepared for the squeegee device in accordance with a plurality of types of attack angles.
However, after replacing the squeegee holder, the position of the lower end of the squeegee changes. During the printing operation, the lower end of the squeegee is in sliding contact with the screen mask. Therefore, the position of the squeegee lower end (horizontal position and vertical position) is extremely important. If the horizontal position of the squeegee lower end before and after replacing the squeegee holder differs, a start position and an end position both shift when the squeegee moves in the horizontal direction. Therefore, when performing the tooling change it is necessary to correct the start position and the end position. More specifically, the start position and the end position of the horizontal movement track of the device body need to be reset.
Also, if the vertical position of the squeegee lower end before and after replacing the squeegee holder differs, the pressing force of the squeegee on the screen mask changes. Therefore, when performing the tooling change it is necessary to correct the pressing force of the squeegee. More specifically, the amount the device body is lowered needs to be reset.
Thus, when adjusting the attack angle of the squeegee during the tooling change, it is necessary to replace the squeegee holder. Work to replace the squeegee holder is accompanied by a need to reset the horizontal movement track, the lowering amount, and the like of the device body.
Japanese Patent Application Publication No. JP-A-H10-157069 describes a screen printing machine that can adjust an attack angle of an oblique blade during the printing operation in order to automatically and constantly maintain a back pressure received by the oblique blade from a solder. Paragraph [0019] of JP-A-H10-157069 describes the oblique blade pivoting generally around a lower end thereof during the printing operation. Regarding this point, similar to the oblique blade during the printing operation, if the squeegee were also to pivot generally around a lower end thereof during the tooling change, the position of the lower end of the squeegee would generally not move.
However, the pivoting mechanism of the oblique blade described in JP-A-H10-157069 cannot be applied to the pivoting of the squeegee during the tooling change. This is because the pivoting of the oblique blade can only occur during the printing operation. In other words, during the printing operation, the lower end of the oblique blade is in sliding contact with the upper surface of the screen mask. In addition, a scraping squeegee is arranged rearward in the sliding direction of the lower end of the oblique blade. Meanwhile, a solder is arranged forward in the sliding direction of the lower end of the oblique blade. Therefore, advancement of the oblique blade is accompanied by the lower end of the oblique blade being pressed into a corner portion between the screen mask and the scraping squeegee. Accordingly, the oblique blade can pivot generally around the lower end thereof. Conversely, the oblique blade cannot pivot in a fixed track when the oblique blade is not pressed in contact with the upper surface of the screen mask, and when the oblique blade is not in contact with the solder.
Thus, the screen printing machine described in JP-A-H10-157069 is not provided with a member for securing the pivot track of the oblique blade. The pivoting mechanism of the oblique blade described in JP-A-H10-157069 is achieved on the presumption of a peripheral state of the oblique blade during the printing operation, and thus cannot be applied to the pivoting of the squeegee during the tooling change.